Design by Contract is a systematic approach to specifying and implementing object-oriented software elements based on precisely defined obligations between them. This is the first practical, example-centered guide to using Design by Contract. The authors introduce powerful design principles for writing good contracts and supporting guidelines -- and demonstrate those principles with real-world Java and Eiffel code examples. They review the fundamentals of Design by Contract -- preconditions, postconditions and invariants -- and presenting a real-world example. Next, drawing on their unparalleled experience with Design by Contract, they present six powerful design principles -- each with a clear statement of goals, rationale, examples in both Java and Eiffel, and supporting notes. Developers will learn how to strengthen their components' internal support for contracts; how to use contracts to specify subclasses whose objects can safely be substituted for superclass objects; how to
extend contract to specify and check properties that remain unchanged; and how to use contracts in analysis-level models. The book concludes by summarizing key principles and presenting a realistic cost/benefit analysis of their use.